The Adult Respiratory Distress Syndrome (ARDS) which affects approximately 150,000 individuals in the United States annually, is characterized by an acute deterioration of lung function in individuals who are already clinically ill. Several lines of evidence suggest that neutrophils may influence the initiation and /or severity of the acute lung injury. Interleukin-8 (IL-8) is an important mediator of acute inflammation because it is both a chemotactic and activating factor for neutrophils. There are elevated concentrations of IL-9 in the distal airspaces of most patients with ARDS. These elevated IL-8 concentrations are correlated with the number of neutrophils as well as the mortality rate, a correlation not paralleled by total protein concentration in the airspaces. Sepsis is the most common and lethal predisposing clinical condition for ARDS, both Gram-negative and - positive bacteria in the bloodstream are capable of inducing diffuse lung injury. The are significantly higher concentrations of IL-8 in the pulmonary edema fluid of patients with ARDS from sepsis than from ARDS in the absence of sepsis. A significant proportion of patients with ARDS have an underlying S.aureus infection, and at least two toxins from S.aureus can stimulate the production of IL-8 by human alveolar macrophages. In these studies we will determine which cells from the lung environment are able to produce IL-8 in response to staphylococcal toxins. First this will be assessed in vitro using different cell types in culture and analyzing the media for the presence of IL-8 protein and activity. The purified toxin will then be administered intravenously to rabbits (to mimic a S.aureus infection of non-pulmonary origin), and the ability of the toxin to induce an increase in IL-8 accumulation in the alveolar spaces and/or lung injury will be determined. The lungs will then be examined with immunocytochemical and in situ hybridization techniques to determine which cells are stimulated by the toxins to produce IL-8 in vivo. Furthermore, using specific peptide inhibitors of the IL-8 receptors, and antisense oligonucleotide inhibitors of IL-8 production, we will be able to determine the role of IL-8 in the development of the injury. We will then use genetic knockouts in S.aureus to determine if specifically inhibiting the toxin production by the bacteria prevents the bacteria from injuring the lung. These studies will reveal the involvement of staphylococcal toxins and IL-8 in the lung injury associated with ARDS. If there is a causative relationship between IL-08 and ARDS, pharmacological control of the expression and/or function of this important cytokine, using the peptides and oligonucleotides which we have developed, may reduce the greater that 50% mortality rate associated with this syndrome.